Electric fuse having prismatic casing



y 1963 'F. J. KOZACKA ELECTRIC FUSE HAVING PRISMATIC CASING Filed Sept. 7. 1967 I FIG. I

mveuron: FREDERICK J. KOZACKA Mow United States Patent 3,382,335 ELECTRIC FUSE HAVING PRISMATIC CASING Frederick J. Kozacka, Southampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Sept. 7, 1967, Ser. No. 666,188 3 Claims. (Cl. 200-120) ABSTRACT OF THE DISCLOSURE An electric fuse in a prismatic casing containing both arc-quench filler and fusible elements conductively connected at each end to terminal plates by 90 degree bends for close fit to the plates. The ends of the fusible elements engage recesses in edges of the plates and are spotwelded thereto.

Background of invention Available space conditions make it sometime necessary or desirable to resort to prismatic fuse casings having substantially planar outer surfaces, and an internal bore, rather than applying the more conventional fuse casings whose outer surface is cylindrical. Casings of the first mentioned type lend themselves well to fabrication by inorganic materials which are heat resistant, and heatshock resistant. Hence prismatic casings having planar outer surfaces and an internal bore are being used in applications requiring heat resistance, and heat-shock resistance.

The present invention is more particularly intended for, though not limited to, fuses having prismatic multibore casings made of asbestos cement, as disclosed and claimed in U.S. Patent 3,291,940 to Frederick J. Kozacka et al., High Interrupting Capacity Fuses Having Casings of Inorganic Material, Dec. 13, 1966.

Fuses having prismatic fuse casings include substantially plate-shaped terminal elements taking the place, and performing the functions of the cylindrical ferrules used in connection with conventional fuses having cylindrical casings. These terminal plates are conductively interconnected by the fusible element, or elements, which are arranged inside of the casing. This invention relates to a novel and improved way of conductively connecting the ends of the fusible element, or fusible elements, to the terminal plates without impairing the mechanical integrity of the latter, and without providing the terminal plates with bores or the like for the passage of the ends of the fusible element from the inside of the casing to the outside thereof, as shown in the aforementioned U.S. patent to Frederick J. Kozacka et al.

Summary of invention Fuses embodying this invention include a prismatic casing of insulating material haivng substantially planar outer surfaces and at least one internal bore filled with a pulverulent arc-quenching filler. A fuse link is arranged inside said bore and submersed in said arc-quenching filler. The fuse link has a perforated center portion, and two pairs of connector tabs. Each pair of said two pairs of connector tabs extends from one end of said center portion of said fuse link. A pair of terminal plates covers opposite surfaces of said prismatic casing, and closes the ends of said internal bore. The aforementioned two pairs of connector tabs are sandwiched between said pair of terminal plates and said opposite surfaces of said prismatic casing, they have bends of about 90 degrees immediately adjacent the outer surface of said prismatic casing, and the ends of said two pairs of connector tabs immediately adjacent said outer surface of said prismatic casing abut against edge portions of said pair of terminal plates and are conductively connected to said edge portions 3,382,335 Patented May 7, 1968 Brief description of drawings Description of preferred embodiment of invention Referring now to the drawings, numeral 1 has been applied to indicate a prismatic casing of insulating material having substantially planar outer surfaces and two internal cylindrical bores 1a. Casing 1 may be of any suitable ceramic material, eg steatite. It is, however, preferably made of asbestos cement for the reasons stated in the aforementioned U.S. Patent 3,291,940, including the possibility of maintaining closer tolerances than those that can be maintained with fired ceramics, the possibility of using fasteners which are not applicable in connection with fired ceramics, and the relative ease of manufacturing relatively small batches in order to fill specific needs. Bores 1a are filled with a pulverulent arc-quenching filler 2, preferably quartz sand. A ribbon fuse link 3 is arranged in each bore 1a and submersed in the arc-quenching filler 2. Fuse links 3 have substantially the same geometry as the fuse links disclosed and claimed in U.S. Patent 3,261,950 to Frederick J. Kozacka, Time-Lag Fuses Having High Termal Efficiency, July 19, 1966; U.S. Patent 3,261,952 to Frederick J. Kozacka, Time-Lag Fuse With Ribbon Fuse Link Having Two Systems of Bends, July 19, 1966; U.S. Patent 3,291,943 to Frederick J. Kozacka, Time-Lag Fuse With Ribbon Fuse Link Folded in Longitudinal and Transverse Direction, Apr. 11, 1967; and U.S. Patent 3,319,028 to Frederick J. Kozacka, Springless Time Lag Fuse for Motor Circuits, May 9, 1967 Reference may be had to these patents in regard to details of the preferred fuse link intended for applications requiring blowing at protracted overloads following predetermined time-lags. The structure of the fuse link 3 shown includes a perforated center potrion 3a and two pairs of connector tabs 3b. Each pair of the two pairs of connector tabs 3b extends from the ends of the aforementioned center portion 3a of each fuse link 3. The center portion 3a of fuse link 3 supports an overlay 4 of a metal which has a lower melting point than the melting point of metal of which fuse link 3 consists, and capable of severing fuse link 3 by a metallurgical reaction or diffusion process on the occurrence of protracted overloads of inadmissible duration. Fuse link 3 may be of copper, or silver, and overlay 4 of tin. Overlay 4 is preferably arranged in the fashion disclosed and claimed in U.S. Patent 2,988,620 to Frederick J. Kozacka, Time- Lag Fuse, June 13, 1961. As shown in FIGS. 1 to 3 a pair of terminal plates 5 covers opposite surfaces of prismatic casing 1, and closes the ends of the two internal bores 1a thereof. Gaskets 6 of a fibrous heat resistant material, preferably asbestos, are interposed between the aforementioned opposite end surfaces of casing 1 and terminal plates 5. The connector tabs 3b are bent out of their general plane which extends parallel to the axis of each bore 1a, and are sandwiched between the opposite end surfaces of prismatic casing 1 and the terminal plates 5, by which these surfaces are covered. The connector tabs 311 have bends 3c of about degrees immediately adjacent the outer surface of prismatic housing 1 and the ends of connector tabs 3b abut against edge portions 5a of terminal plates 5, and are conductively connected with, e.g., spot-welded to, these edge portions. Edge portions 5a of terminal plates 5 are preferably provided with substantially U-shaped recesses 5b for positioning the ends 3d of connector tabs 3b remote from the center portion 3a of fuse link 3. The aforementioned ends 3d of connector tabs 3b engage recesses b and are spot-welded to the web portions of recesses 5b.

It will be apparent from the foregoing that the terminal plates 5 do not have any bores, or the like, for the passage of the fuse links from the inside of the casing 1 to the .outside thereof to make it possible to establish conductive connections between fuse links 3 and terminal plates 5 on the outside of the casing. The small lateral incisions or recesses 5b in terminal plates 5 for positioning the ends 3c of connector tabs 3b of fuse links 3 do not impair the mechanical integrity of terminal plates 5.

Terminal plates 5 may be provided with any desired means for placing the fuse into a fuse holder. In the embodiment of the invention shown each of terminal plates 5 are provided with an upstanding flange 50 having a hole 5d which makes it possible to screw the upstanding flange 50 against a cooperating contact plate of a fuse holder (not shown).

Terminal plates 5 may be secured to casing 1 by various fastener means among which self-tapping screws 7 are preferred.

Having disclosed a preferred embodiment of the invention, it is desired that the same be not limited to the particular structure disclosed. It will be obvious to any person skilled in the art that many changes and modifications may be made without departing from the. spirit and the scope of the invention as set forth in the appended claims.

I claim as my invention:

1. An electric fuse including (a) a prismatic casing of insulating material having substantially planar outer surfaces and an internal bore;

(b) a pulverulent arc-quenching filler inside said bore;

(c) a ribbon fuse link arranged inside said bore and submersed in said arc-quenching filler, said fuse link having a perforated center portion and two pairs of connector tabs, each pair of said two pairs of connector tabs extending from one of the ends of said center portion; and

(d) a pair of terminal plates covering opposite surfaces of said prismatic. casing and closing the ends of said internal bore thereof, said two pairs of connector tabs being sandwiched between said pair of terminal plates and said opposite surfaces of said prismatic casing, said two pairs of connector tabs having bends of about degrees immediately ad jacent the outer surface of said prismatic casing, and the ends of said two pairs of connector tabs immediately adjacent said outer surface of said prismatic casing abutting against edge portions of said pair of terminal plates and being conductively connected to said edge portions of said pair of terminal plates.

2. An electric fuse as specified in claim 1 wherein said edge portions of said terminal plates are provided with substantially U-shaped recesses for positioning the ends of said two pairs of connector tabs remote from said center portion of said fuse link, and wherein said two pairs of connector tabs engage said recesses and are welded to the Web portions of said recesses 3. An electric fuse as specified in claim 1 wherein said casing consists of asbestos cement.

References Cited UNITED STATES PATENTS 2,148,803 2/1939 Bussmann 200l35 3,029,328 4/1962 Kozacka 200 3,143,615 8/1964 Kozacka 200120 3,341,674 9/1967 Jacobs 200 XR 3,291,940 12/1966 Kozacka et a1. 200-120 FOREIGN PATENTS 589,554 3/1959 Italy.

596,875 5/1934 Germany.

644,853 5/ 1937 Germany.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

